The present invention relates to a vaporization injector in an instrument for gas chromatography analysis.
Vaporization injectors are well-known in themselves and composed of a so-called vaporization chamber, generally in the form of a heated cylinder, connected on one side (usually the bottom) to a capillary gas chromatography column and closed on the other side (top) by a septum destined to be perforated by a needle for injecting the sample. This needle is fitted to a syringe containing a measured quantity of sample, composed of the substance to be analysed and a solvent for this. The needle is inserted, perforating the septum, to a pre-established position inside the vaporization chamber and the liquid sample is thrust by the syringe piston into this chamber, where it vaporizes before being carried to the gas chromatography column by the carrier gas, which is generally fed in on the same side, namely the top part of the chamber. Depending on the methods chosen, the sample may either be injected into the column partially (split mode) or totally (splitless mode).
In any case, it is important for the sample to vaporize optimally and totally in the vaporization chamber, where it is temporarily stored before being sent to the column. The current trend to increase the sample volumes injected creates some problems, especially in splitless vaporization injection, specifically relevant to the capacity of the vaporization chamber and filling this in an optimum manner. In fact, the transversal dimensions (diameter) of the chamber cannot be increased beyond certain limits for reasons related to vapours mixing with the carrier gas and complete transfer of the sample to the column. On the other hand, an increase in the capacity of the chamber by increasing its length does not have any significant effects, as the vaporized sample tends to be stored in the chamber above the injection point, namely from the tip of the injection needle. Nonetheless, the length of the injection needle is necessarily limited, both for reasons related to mechanical resistance and for reasons concerning excessive dead volume, represented by the internal channel of the needle.
Having stated this, it is now an object of the present invention to provide a vaporization injector, especially of the splitless type, in which the aforesaid limits in the increase of the capacity of the vaporization chamber by means of increasing the longitudinal dimensions of this chamber are overcome and it is thus possible to proportion the vaporization chamber optimally, to obtain temporary storage also of large amounts of sample.
A further object of the invention is to obtain in a reliable manner a cloud of vapour in a specific portion inside the vaporization chamber, contrary to what occurs in the known technique. According to the invention, the aforesaid objects are implemented by means of a vaporization injector as claimed in claim 1.
The aforesaid and other peculiarities and features of the invention shall now be illustrated in greater detail, with reference to embodiments given merely as an example and schematised in the enclosed drawings in which:
FIG. 1 is a schematic cross-section of a vaporization injector according to the currently known technique;
FIG. 2 is a schematic cross-section of a first embodiment of the invention;
FIG. 3 is a schematic cross-section of a second embodiment of the invention;
FIG. 4 is a schematic representation of a further embodiment of the invention.